The invention relates to aqueous binder dispersions for aqueous coating compositions based on polyurethanes, which can be (meth)acrylated, comprising water-insoluble cellulose esters. It also relates to processes for their preparation and processes for multilayer lacquering using the coating compositions, in particular as a water-based lacquer in processes for the production of decorative multilayer lacquerings of the water-based lacquer/clear lacquer type.
Base lacquers which are based on organic solvents, comprise cellulose esters, such as cellulose acetobutyrate, and are suitable for the production of decorative multilayer lacquerings of the base lacquer/clear lacquer type are known. Cellulose esters impart particular rheological properties to base lacquers based on organic solvents, and in the case of effect base lacquers these lead to a favourable enhancement of the effect within the finished two-layer effect lacquering.
Water-based lacquers comprising water-insoluble cellulose esters are known from EP-A-0 069 936 and from WO 97/49739. EP-A-0 069 936 describes dispersions of cellulose esters in water which are suitable as binders in water-based lacquers and are prepared by copolymerization of a mixture of a water-soluble resin from the group consisting of polyester resins, acrylic resins and alkyd resins and alpha,beta-ethylenically unsaturated monomers in the presence of the dissolved cellulose esters, the cellulose ester content, based on the total solids content of the dispersion, being between 5 and 40%. WO 97/49739 describes dispersions which are suitable as binders in water-based lacquers and comprise at least 5 wt. %, preferably 10 to 30 wt. % of cellulose esters, based on the resin solids of the dispersion, the dispersions being those which are based on vinyl polymers and are prepared by copolymerization of previously prepared aqueous emulsions of cellulose esters dissolved in a mixture of vinyl monomers. The vinyl monomers here include polyunsaturated vinyl monomers.
The water-based lacquers of the prior art comprising water-insoluble cellulose esters have a low processing solids content compared with corresponding water-based lacquers comprising no water-insoluble cellulose esters. It has furthermore been found that the cellulose esters contained in the known base lacquer layers weaken the weathering resistance of base lacquer/clear lacquer two-layer lacquerings.
The object of the invention is to provide aqueous coating compositions which have a rheologically active content of cellulose esters, do not have the above disadvantages and are suitable in particular for multilayer lacquerings, in particular for producing colour- and/or effect-imparting base lacquer layers.